This invention generally relates to a magnetometer for a torque sensor. More particularly, this invention relates to a magnetometer including several coils disposed relative to each for measuring torque related divergent magnetic fields.
A non-contact force sensor includes a force transducer element that responds to the application of force by generating a magnetic field. The generated magnetic field is then detected by a magnetometer. The force transducer element typically includes a magnetoelastic material that responds to the application of force by generating a magnetic field. The application of force to the magnetoelastic material creates shear stresses within the magnetized regions causing the direction of the magnet field generated by the force transducer element to shift from a substantially circumferential direction to a helical direction. The helical shifting of the magnetic field is detected as an axial component of the magnetic field. The axial component of the magnetic field is proportional to the applied force and provides an accurate and reliable indication of torque applied to a torque element.
Sensing of the magnetic field and specifically the axial components of the distortions in the magnetic field caused by force is accomplished through the use of a magnetometer or magnetic field sensor. A commonly used type of magnetic field sensor is a flux gate sensor, which is fabricated as a coil of magnet wire that generates a magnetic field to magnetically saturate a core of magnetically saturatable material. The coil is energized by an alternating current that provides periodic magnetic saturation of the core. The magnetic field produced by the force transducer is superimposed on the periodic magnetic field generated by the coils. The superimposing the magnetic field produced by the torque transducer shaft creates an asymmetry in the magnetic saturation of the coils. Changes in the inductance of the coils due to the magnetic saturation results in a voltage that is induced to the coils. It is this voltage that is measured to determine the amplitude and direction of force applied to the force transducer element.
It is commonly observed within magnetoelastic torque transducers a magnetic hysteretic effect wherein the zero-torque magnetic field emanating from the transducer does not return to zero amplitude following the application and removal of a stimulus torque. It is observed that the amplitude of the magnetic hysteresis resulting from the application of a force varies with the square of the magnetic flux passing within the transducer element, as a consequence of the magnetic field generated in the transducer from this force.
Consequently it is an object of the current invention to provide a means of attenuating the effects of magnetic hysteresis within the transducer through the operation of the magnetometer.